Design of Neutral Ni[N,N] Catalysts for High-Density Polyethylene Formation: Insights into Catalyst Deactivation
Bence Szabó, Lennox W. Stewart, Georgina M. Rosair, Stephen M. Mansell
TL;DR
Researchers designed new nickel catalysts for making high-density polyethylene and studied how these catalysts break down during polymerization.
Contribution
The study introduces neutral Ni[N,N] catalysts and structurally characterizes their deactivation pathway via C–H activation for the first time.
Findings
Neutral Ni[N,N] catalysts produced high-density polyethylene with melting points up to 140 °C.
Catalyst deactivation via C–H activation was observed and structurally confirmed using NMR and X-ray diffraction.
B(C6F5)3 was found essential for ethylene polymerization despite increased steric bulk.
Abstract
Neutral Ni[N,O] and cationic Ni[N,N] complexes are two prominent classes of catalysts for the polymerization of ethylene. We report the amalgamation of these motifs and describe the synthesis and catalytic activity of two neutral Ni[N,N] catalysts [Ni(Ph)(L)(PPh3)], where L = 2-(arylamido)-5-methylcyclopent-2-en-1-arylimine (7) or 2-(arylamido)-cyclohex-2-en-1-arylimine (8); aryl is the ubiquitous 2,6-diisopropylphenyl group (Dipp). Despite the increased steric bulk, ethylene polymerization was only achieved using B(C6F5)3 as an activator, forming high-density polyethylene at 0 °C with T m up to 140 °C, in contrast to the branched polymers characterized by lower melting points that are more typically formed using nickel catalysts. Surprisingly, both complexes undergo C–H activation over days at room temperature, eliminating benzene and forming a cyclometalated Ni(II) complex…
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Taxonomy
TopicsOrganometallic Complex Synthesis and Catalysis · Catalytic Cross-Coupling Reactions · Synthetic Organic Chemistry Methods